In the case of integrated circuits, a distinction is drawn between the internal supply voltage and the external supply voltage. The external supply voltage is applied to the input connection of the voltage regulator. The output connection of the voltage regulator, which can be connected to the circuit arrangement, applies the internal supply voltage to this circuit arrangement. The magnitude of the internal supply voltage is in this case governed by the requirements of the circuit arrangement. The internal supply voltage is normally lower than the external supply voltage. In consequence, the voltage regulator carries out the task of “transforming” the external supply voltage to the internal supply voltage. In this case, the internal supply voltage must be kept as constant as possible irrespective of voltage fluctuations of the external supply voltage, in order to make it possible to ensure the operation of the circuit arrangement that is to be supplied.
As the level of technological integration of the component of the circuit arrangement to be supplied increases, the internal supply voltage decreases. Since, at the same time, the maximum permissible external voltage range is extended on the basis of the predetermined standards (for example Global System for Mobile communication GSM or International Standard Organization ISO), the requirements for the voltage regulator to provide a constant internal supply voltage are becoming more stringent.
One problem in particular is to compensate for voltage spikes on the external supply voltage.
Firstly, the voltage spikes may increase as the external voltage range becomes wider. Secondly, a reduced internal supply voltage must be provided because of the technological integration level of the components of the circuit arrangement, as mentioned above. In this case, the same voltage fluctuations, that is to say their absolute value, produce greater effects as the internal supply voltage is decreased, since the relative change is then greater. Conventional voltage regulators are frequently therefore no longer able to generate a sufficiently constant internal supply voltage when major external voltage fluctuations occur and the required internal supply voltages are low.
In principle, two different types of voltage regulators are known from the prior art.
Firstly, there are integrated voltage regulators with p-channel series regulating transistors, which draw a small amount of current but are highly sensitive to voltage. The high voltage sensitivity is due to the fact that the external supply voltage is connected to the source connection of the p-channel series regulating transistor. p-channel series channel transistors are currently used in voltage regulators for integrated circuits for use in smart cards.
Furthermore, voltage regulators with n-channel series regulating transistors are known. These have little sensitivity to voltage, since the external supply voltage is connected to the drain connection of the n-channel series regulating transistor. However, this type has the disadvantage that the current draw is increased, due to the requirement for an additional oscillator and an additional voltage pump for driving the gate of the n-channel transistor. As a result of this, voltage regulators with an n-channel series regulating transistor require an increased current draw, particularly in a rest state. This results in contravention of the GSM and ISO standards mentioned above.